Measuring Mytilus californianus: an Addendum to Campbell and Braje (2015) and Singh and McKechnie (2015) including commentary and an integration of data

Archaeological and Contemporary Evidence Indicates Low Sea Otter Prevalence on the Pacific Northwest Coast During the Late Holocene

“…We established an asymptotic relationship between modern mussel umbo thickness and total shell length (Figure 2 b). Specifically, umbo thickness explained 89% of the variation in total shell length ( y = 544.81x / 24.75 + x, R 2 = 0.89, n = 313 mussels), improving upon a linear fit ( y = 13.3 + 14.5x, R 2 = 0.87, Figure S2) and a previously published linear regression by 5% (McKechnie and others 2015 ; R 2 = 0.84). We used this asymptotic relationship to estimate the total shell length of our archaeological mussel fragments due to its higher R 2 and the more conservative length estimates it predicts for thicker umbos compared to the linear model.…”

“…To determine total California mussel shell length from fragmentary ancient specimens, we expanded on an existing valve length to umbo thickness relationship established for modern mussels (McKechnie and others 2015 ) by including large mussel shells (130–223 mm, n = 50) collected from Barkley Sound, BC, in 2018. This contemporary morphometric relationship was chosen to estimate ancient shell length because umbos are the most robust portion of the mussel preserved in midden deposits, and represent the origin of shell growth, a strong predictor of full shell length (Seed 1968 ; Ford and others 2010 ).…”

“…This contemporary morphometric relationship was chosen to estimate ancient shell length because umbos are the most robust portion of the mussel preserved in midden deposits, and represent the origin of shell growth, a strong predictor of full shell length (Seed 1968 ; Ford and others 2010 ). Umbo thickness was measured from the tip of the umbo to the inside of the hinge using digital calipers (Figure 2 a), whereas shell length was measured from the outer umbo to the point on the shell’s end that measures the longest valve dimension (for detailed methods see McKechnie and others ( 2015 ) and Singh and McKechnie ( 2015 )). Inter-observer measurement discrepancy and error were minimized by using a consistent measurement approach, carried out by two trained observers.…”

“…Moreover, ancient California mussels are ubiquitous in archaeological sediments along the Northwest Coast of North America (Wessen 1988 ; Moss 1993 ; McKechnie 2014 ) throughout the Holocene. Their ubiquity has led to the quantification of several morphometric relationships (McKechnie and others 2015 ), allowing full shell length to be derived from shell fragments, which in turn enables the reconstruction of past mussel size structure (Braje and others 2018 ).…”

Proxy Measurements of California Mussel Valve Length

“…) measurements obtained from valve fragments, and we propose several new metrical proxies that have the potential of utilizing a large proportion of valve fragments occurring in mussel shell assemblages. Our efforts build on those of Singh and McKechnie (2015) and Campbell and Braje (2015), who recently gave extensive attention to this topic (see also McKechnie et al 2015). We also evaluate a visual technique developed by White (1989:132-133) and utilized by a number of archaeologists working in California.…”